The invention relates to a medical instrument, and in particular to a generator for power generation for high-frequency surgery.
1. Field of the Invention
In the case of medical instruments, a matter of foremost concern, apart from that of the actual treatment, is the safety of patients and of persons performing the treatment. Many medical instruments act on a patient by means of electrical or mechanical energy, or require internal electrical or mechanical energy for a performance of their functions. Because of these forms of energy, any faulty handling or malfunction of an instrument may endanger patients or persons performing a treatment. The potential danger will be described by using a high-frequency generator for surgery as an example.
In high-frequency surgery, human or animal body tissue is cut or coagulated by means of an electrical current. High-frequency surgery can be applied with extreme advantage, particularly in combination with endoscopic operating techniques.
It is the object of generators for high-frequency surgery to provide electrical energy for high frequency surgery, so that a desired result of a surgical operation can be achieved. In order to minimize muscle and nerve irritation, generators for high-frequency surgery supply high-frequency energy in a frequency range above 300 kHz. This high frequency energy is usually applied to tissue by means of an electrode. Strong heating of the tissue surrounding the electrode occurs at the point of application. If high energy is applied within a short period of time, this leads to a vaporization of cell fluid and a bursting of cells, so that the group of cells surrounding the electrode is disintegrated. The electrode can move almost freely through the tissue. If less energy is supplied for a long period of time, this leads to a coagulation of the tissue, i.e. to a congealing of protein. In this case, the cells die off and form a viscous mass.
As far as an introduction of high frequency energy is concerned, a basic distinction is made between two arrangements.
In a monopolar arrangement, a cutting or coagulating electrode having a small surface for introducing current is disposed at the site of a surgical operation, and a “neutral” electrode having a large surface for conducting current away is disposed at a different site of the body of a patient. Here the electrode surface is made to be large enough for no appreciable heat to be developed at the electrode.
A bipolar arrangement comprises a divided electrode with which a current is introduced into and a current is conducted away from the site of the operation.
A high-frequency generator can therefore draw considerable amounts of energy from a line, store it internally, and supply it at its output even for a long period of time, for the purpose of cutting or coagulating tissue. High safety demands are made on high-frequency generators for surgery, so that any inadvertent emission of power to the output can be avoided with highest reliability. In the same way, even in a case of a fault occurring for the first time, no higher power should be emitted than that pre-selected by an operator.
2. Description of the Prior Art
Thus, U.S. Pat. No. 6,142,992 provides for a limitation of the power, which automatically limits the emitted power of a generator when the electrode makes no contact with the tissue.
The Patent DE 197 14 972 describes a monitoring of the neutral electrode. This prevents faulty handling when the neutral electrode is applied.
Safety devices known in prior art relate to a monitoring of outer generator functions and to protection from faulty handling. However, protection from internal malfunction of the instrument is just as important as protection from outer faulty handling.
Most of the medical instruments known today are controlled by a central control computer or microprocessor, also known as a controller. Known methods of safety checks, such as interrogation schedules additionally incorporated in the software of the main controller, do not safeguard against a failure of the controller and also not against errors of programming. A multiple redundant arrangement of identical controllers requires a very high outlay of material, and also does not provide a safeguard from programming errors.